1. Field of the Invention
The present invention relates to a valve structure including a wall member having a valve hole, a valve element and a retainer having a retaining surface, by which bending of the valve member is restricted by receiving the rear surface of the valve member.
2. Description of the Related Art
Japanese Unexamined Patent Publication (Kokai) No. 7-151264 discloses a piston type compressor having a discharge valve assembly. The discharge valve assembly includes a discharge valve member having a fixed root portion and a free, distal end capable of opening and closing a discharge port, and a valve stop (retainer) opposed to the valve member so that the valve member cannot be opened beyond a predetermined limit. In this prior art, in order to reduce noise caused when the valve member opens and collides against the retainer in the case of discharging compressed gas from the piston cylinder bore, the profile of the retainer is made to correspond to a bending shape of the valve member in the case where the maximum stress is given to the valve member. That is, noise caused when the valve member and the retainer collide with each other is suppressed as follows. When the profile of the retainer is designed so that the stress given to the valve member at each contact point can reach the maximum allowable stress, the positional energy of the valve member becomes maximum, and on the other hand, the valve member collides with the retainer at the moment the kinetic energy becomes minimum. In this way, noise caused when the members collide with each other can be suppressed. In brief, in this prior art, the profile of the retainer is made to agree with a freely bent shape of the valve member when the distal end portion of the valve member is pushed up in the vertical direction from the closed position.
However, in the valve structure including the retainer, there is an essential problem to be solved before solving the problem of noise caused when the valve and the retainer collide with each other. The problem is to enhance durability of the valve structure which is repeatedly opened and closed. To be specific, the enhancement of durability of the valve structure is to prevent an occurrence of breakage in which the valve member is broken at its root, and an occurrence of damage in which the valve member and/or the wall member is damaged by the collision of the valve member against the wall member forming the discharge hole (valve hole). In view of the above essential technical demands for the valve structure, the above prior art is not provided with sufficiently high durability. That is, according to the above prior art, there is a possibility of the fatigue failure on bending (break of the root) of the valve member, and also there is a possibility of the fatigue failure on impact (break) in the case of opening and closing the valve member. In other words, there is a technical problem with durability.
It is an object of the present invention to provide a valve structure, which can enhance durability with respect to the fatigue failure on bending of the valve member and the fatigue failure on impact.
According to the present invention, there is provided a valve structure comprising a wall member having a surface and a valve hole opening in said surface, said valve hole having a center, a flexible valve element having a first portion lying on said surface of said wall member and a second portion bendable toward and away from said wall member to open and close said valve hole, and a retainer element having a retaining surface to restrict deformation of said valve element when said valve element is bent toward said retainer element.
The retaining surface of said retainer element has a profile containing a coordinate (xxe2x80x2, f(xxe2x80x2)xe2x88x92K) within an abscissa range between an origin and said center of said valve hole so that said profile is displaced toward said wall member with respect to a freely bent shape of said valve element.
In this case, the profile is expressed in a two-dimensional coordinate system (x, y) having an X axis extending parallel to the surface of the wall member in the direction from the first portion toward the second portion of the valve element, a Y axis extending perpendicular to the X axis in the direction away from the wall member, and the origin near the first portion of the valve element, the origin corresponding to a start point of the profile; the freely bent shape is represented by coordinates (x, f(x)) obtained by pushing the valve element in the Y-axis direction at an abscissa position corresponding to the center of the valve element so as to urge the valve element away from the wall member; L is a distance from the origin to the center of the valve hole; H is a distance between the valve element and the wall member at an abscissa position of x=L in the freely bent shape; xxe2x80x2 is an abscissa value satisfying the relationship of f(xxe2x80x2)=H/2 between the origin and the center of the valve hole; and K (0 less than K) is a displaced value in the Y-axis direction.
The present invention also provides a compressor having a valve structure having an identical feature to that of the above described valve structure.
In this valve structure, a y coordinate value of the profile of the retaining surface of the retainer corresponding to an x coordinate value (xxe2x80x2) satisfying the relationship of f(xxe2x80x2)=H/2 between the origin of the two dimensional coordinate system (x, y) and the center of the valve hole is smaller than a y coordinate value of the freely bent shape of the valve element by a positive displaced value K. As a result, in the abscissa coordinate range from the origin to the center of the valve hole, the profile of the retaining surface of the retainer is displaced toward the wall member with respect to the freely bent shape (the estimated line of the valve element). Therefore, when the valve element is bent toward the retainer when opening the valve, a portion close to the root of the valve element gradually comes into contact with the retaining surface of the retainer. In this case, as the valve element is bent, the contact point (fulcrum of bend) of the rear surface of the valve element with the retaining surface of the retainer gradually moves from the origin to the distal end portion of the valve element. Consequently, according to this valve structure, when the valve element is opened, the concentration of stress upon the root of the valve element located at the coordinate origin (start point of the profile of the retaining surface of the retainer) can be avoided or reduced. Therefore, durability of the valve element with respect to the fatigue failure of bend of the valve element and the fatigue failure of impact can be enhanced. On the other hand, if a profile agreeing with the freely bent shape of the valve element is adopted as the profile of the retaining surface of the retainer, that is, if the prior art is adopted, the fulcrum point of bending of the valve element is always located at the origin of the two-dimensional coordinate system (x, y) and is not moved at all. Therefore, the stress concentration upon the root of the valve member cannot be avoided.
In the preferred form of the present invention, the distance between the retaining surface of the retainer and the wall member at the abscissa coordinate of (x=L) corresponding to the center of the valve hole is H (=f(L)), which agrees with the profile in the freely bent shape. The preferable range of the displaced value K is in the range from 3% to 20% of the distance H. The critical meanings of the upper and the lower limit will be made clear later. The profile of the retaining surface of the retainer in the abscissa range from the origin of the coordinate to the center of the valve hole can be smoothly continued to the profile of the retaining surface of the retainer in the abscissa range beyond the center of the valve hole.